RU2207525C2 - Method for measuring light fluxes and apparatus for performing the same - Google Patents

Abstract

FIELD: measuring of light fluxes (photometry, pyrometry), pickups for measuring IR-irradiation, visual and optical UV-irradiation, flame and temperature. SUBSTANCE: method comprises steps of converting light flux to train of electric pulses whose frequency and duty ratio depend upon intensity of light flux; measuring frequency, duration and duty ratio of pulses for evaluating intensity of light flux. Apparatus for performing the method includes photodiode, amplifying unit and resistor. Apparatus is in the form of RC self-excited oscillator having photodiode, amplifying unit, resistor and capacitor. Photodiode and resistor connected in series with it are connected to frequency setting circuit of self-excited oscillator. Amplifying unit may have two inverters connected in series. Photodiode and resistor connected in series with it are connected by first inlet to inlet of first inverter and by second inlet - to outlet of first inverter. Capacitor is connected between inlet of first and outlet of second inverters. Amplifying unit may have three connected in series inverters. In such case connected in series resistor and photodiode are connected between inlet of first and outlet of third inverters; capacitor is connected between inlet of first and outlet of second inverters. EFFECT: increased dynamic range of measured light fluxes, improved accuracy of measurement. 4 cl, 4 dwg

Description

 The invention relates to the field of photometry and pyrometry and can be used to measure light fluxes of the IR, visible and ultraviolet ranges, and can also be used as flame and temperature sensors.

 A known method of measuring the intensity of light flux, which consists in converting a light detector into an analog electric signal by a photodetector, amplifying this signal and measuring the parameters of the analog signal, which determine the characteristics of light radiation [1]. The disadvantages of the method include low noise immunity, measurement accuracy, as well as a small input dynamic range.

 Also known is a method of measuring the intensity of light radiation [2], in which the signal from the photodetector arrives simultaneously at two amplifiers, the difference in the output signals of which determine the characteristics of the radiation. The method allows to slightly increase the dynamic range of the measured light fluxes, but other disadvantages are also inherent in it.

 Closest to the claimed method is a method of measuring the intensity of light fluxes [3] by converting it into a sequence of electrical pulses, the repetition rate of which depends on the radiation intensity, and measuring the duration of the pulses. The disadvantage of this method is the small input dynamic range. Another disadvantage of this method is the two-stage process of converting an optical signal into a signal frequency. A photodetector converts an optical signal into a voltage, and then this voltage is converted into a sequence of electrical pulses using an analog-to-digital converter. Due to this, the accuracy of measurements is reduced and the circuit is complicated.

 The objective of the invention is to increase the dynamic range of the measured light fluxes, as well as improving the accuracy of the measurement.

 The problem is achieved in that in the method of measuring light fluxes by converting it into a sequence of electrical pulses, the repetition rate of which depends on the intensity of the radiation, and measuring the duration of the pulses, form a sequence in which the frequency and duty cycle depend on the intensity of the flow, additionally measure the duty cycle and according to the results of joint measurements of frequency, duration and duty cycle judge the magnitude of the luminous flux.

 The problem is achieved in that in a device containing a photodiode, an amplifying element, a resistor and a capacitor, a photodiode and a resistor are connected in series and installed in the frequency-setting R-circuit of a self-oscillator or multivibrator. The amplifying element is made on two inverters connected in series. Serially connected photodiode and resistor with the first output are connected to the input, and the second - to the output of the first inverter, and a capacitor is connected between the input of the first and the output of the second inverters. Also, the amplifying element can be made on three inverters connected in series, and a resistor and a photodiode connected in series between the input of the first and the output of the third inverter. A capacitor is also included between the input of the first and the output of the second inverter.

 In FIG. 1 shows a self-oscillator (multivibrator), in the frequency-setting R-circuit of which are connected series-connected photodiode and resistor.

 The device shown in figure 1, contains a self-oscillator (multivibrator), in the frequency-setting R-circuit of which are connected in series connected photodiode 2 (VD1) and resistor 3 (R1). The device operates as follows. The light flux falls on photodiode 2, the intensity of which determines the resistance of the photodiode in the closed state. If there is a voltage at the output of the oscillator 1 corresponding to the closed state of photodiode 2, the process taking place in the oscillator (for example, if it is an RC generator, then charging or discharging the capacitor) will be determined mainly by its value. After the polarity of the voltage at the output of the oscillator 1 changes, the photodiode 2 will be in the open state and the process occurring in the oscillator 1 will be determined mainly by the value of the resistor 3. As a result, the pulse durations corresponding to the open and closed state of the photodiode will be different .

 In FIG. 2 shows a schematic diagram of a device on two inverters. Figure 3 presents the signals at the output of the first inverter at different intensities of the incident light flux. Figure 4 presents a schematic diagram of a device on three inverters.

 The device shown in figure 2, contains a photodiode 2 (VD1), a resistor 3 (R1) connected in series with it, a capacitor 4 (C1) and two inverters 5 and 6 (DD1.1 and DD1.2). In this case, the resistor 3 (R1) is connected to the input of the first inverter 5 (DD1.1), and the photodiode 2 (VD1) is connected to its output (reverse connection is possible), and the capacitor 4 (C1) is connected between the input of the first 5 (DD1.1 ) and the output of the second 6 (DD1.2) inverters.

 The device operates as follows. Suppose that after turning on the power source, the voltage at the output of the first inverter 5 (DD1.1) corresponds to the logic level “1”, and at the output of the second inverter 6 (DD1.2) it corresponds to the logic level “0”. Then, at the initial time, the voltage on the left side of the capacitor 4 (C1) also corresponds to a logical "0". Photodiode 2 (VD1) is in the closed state. Capacitor 4 (C1) starts charging through resistor 3 (R1) and closed photodiode 2 (VD1). The resistance of the closed photodiode 2 (VD1) depends on the intensity of the radiation incident on it, and the higher the light flux, the lower the resistance of the closed photodiode 2 (VD1), the capacitor 4 (C1) is charged faster and the threshold level at the input of the first inverter 5 (DD1) is reached .1). When it is reached, at the output of the first inverter 5 (DD1.1), the signal will correspond to the logic level “0”, and at the input of the second inverter 6 (DD1.2) it will correspond to the logic “1” as a result of an avalanche-like process. In this case, on the left side of the capacitor 4 (C1), the voltage becomes equal to the voltage of the power supply plus the voltage of the threshold level, and photodiode 2 (VD1) goes into the open state. Capacitor 4 (C1) will begin to discharge through resistor 3 (R1) and open photodiode 2 (VD1). The resistance of an open photodiode is several orders of magnitude lower than the resistance of a closed photodiode, and it almost does not depend on the light flux incident on it. Therefore, the discharge process is determined mainly by the resistance value of the resistor 3 (R1) and, to a lesser extent, the resistance of the open photodiode 2 (VD1) and is almost independent of the radiation incident on the photodiode. Then the voltage on the left side of the capacitor 4 (C1) begins to decrease, and when the threshold value at the input of the first inverter 5 (DD1.1) is reached, the voltage at its output will again become "1", and at the output of the second inverter 6 (DD1.2) - "0", and the capacitor 4 (C1) will again begin to charge. The result is a sequence of electric rectangular pulses (digital), in which the frequency and duty cycle of the pulses depends on the intensity of the radiation (figure 3). At the same time, the dynamic range of the measured luminous fluxes is expanded (determined by the operability range of photodiode 2 (VD1)), and accuracy is also improved by measuring three values at once: the frequency, duration and duty cycle of the pulses. In figure 3, signal 7 corresponds to a low intensity of light radiation, and signal 8 is large. Moreover, the duration corresponding to the logical "1" depends on the intensity of light radiation, and the duration corresponding to the logical "0" does not depend on it (for a given inclusion of the polarity of photodiode 2 (VD1)).

 The device in figure 4 also contains a photodiode 2 (VD1), a resistor 3 (R1) and a capacitor 4 (C1) connected in series with it, but three inverters 5 (DD1.1), 6 (DD1.2), 9 (DD1. 3). In this case, the resistor 3 (R1) is also connected to the input of the first inverter 5 (DD1.1), but the photodiode 2 (VD1) is connected to the output of the third 9 (DD1.3). The device works similarly to the device on two inverters, but has better stability, since the charge and discharge of the capacitor 4 (C1) is carried out through the output of the third 9 (DD1.3), and not the first 5 (DD1.1) inverter.

 The proposed devices on two and three inverters were used as sensors of thermal radiation. FD-7G was used as a photodiode.

 Depending on the choice of the capacitor value 4 (C1) and the type of microcircuit DD1, the range of pulse repetition frequencies varied from almost a fraction of Hz to hundreds of kHz.

Sources of information
1. RU 2038474.

 2. RU 2030716.

 3. RU 2014574 (prototype).

Claims (4)

 1. A method for measuring light fluxes by installing a photodetector in a light flux, converting light radiation into a sequence of electrical pulses, the repetition rate of which depends on the intensity of the light flux, and measuring the pulse duration, characterized in that the photodetector, the resistance of which depends on the direction of the current, is fed voltages of different polarity corresponding to the open and closed state of the photodetector form a sequence in which the frequency and duty cycle of the pulses hanging on the flow rate, porosity additionally measured and the results of simultaneous measurements of frequency, duration, and duty cycle is judged on the light flux.  2. A device for measuring light flux containing a photodiode, an amplifying element and a resistor, characterized in that the amplifying element, photodiode, resistor and capacitor form an RC oscillator, the photodiode and resistor connected in series and installed in the frequency-setting R-circuit of the oscillator.  3. The device according to claim 2, characterized in that the amplifying element is made on two inverters connected in series, the photodiode and resistor connected in series with the first output connected to the input, and the second to the output of the first inverter, and a capacitor connected between the input of the first and the output of the second inverter.  4. The device according to claim 2, characterized in that the amplifying element is made on three inverters connected in series, the photodiode and resistor connected in series are connected between the input of the first and the output of the third inverters, and the capacitor is connected between the input of the first and the output of the second inverters.

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